The present invention relates to terminal equipment for measuring its own position, particularly to equipment for measuring distances and positions using the radio waves emitted from base stations fixed on the ground, including CDMA base stations.
The principles of distance measurement using a spread spectrum signal are described using FIG. 9. The station for transmitting the spread spectrum signal transmits this signal in send timing 400. The aforementioned receiving station receives the spread spectrum signal and obtains receive timing 401. Differential time 402 between receive timing 401 and send timing 400 is detected as the propagation time of the spread spectrum signal. The distance between the transmitting station and the receiving station can be calculated by multiplying differential time 402 by the velocity of light. Because of the principles described above, distance measurement using a spread spectrum signal requires the measurement of receive timing 401 at the receiving station.
Next, the principles of position measurement using a spread spectrum signal are described. The distances to individual transmitting stations are measured by the receiving station, subject to the principles described above. The use of the thus-obtained distances between the receiving station and each base station and of the positions of the base stations enables the position of the receiving station to be detected by solving the equation where the position thereof is taken as an unknown quantity. Details of one such detection method are disclosed in, for example, Japanese Laid-Open Patent Publication No. Hei 7-181242 (1995).
To use spread spectrum signals for conducting distance or position measurements in this way, it is necessary to measure the receive timing of the aforementioned spread spectrum signal at the terminal equipment. In Japanese Laid-Open Patent Publication No. Hei 7-181242 (1995), the following method for measuring such receive timing is disclosed: the correlation values between the received signal and the predetermined code series for creating spread spectrum signals (hereinafter, collectively called the PN code) are calculated for each receiving event, and a profile is created that shows the values corresponding to the correlation values in each receiving event (hereinafter, this profile is called the delay profile); wherein an epitomized diagram of the delay profile is shown as 1 in FIG. 10, and the timing where the correlation value becomes a maximum in the delay profile is searched for and the corresponding timing is detected as the timing in which the spread spectrum signal is received. In the example of FIG. 10, xe2x80x9ctprevxe2x80x9d is the receive timing.
During distance measurement and position measurement, it is important to measure the receive timing of the signal wave that has first arrived at the terminal equipment, namely, the incoming wave of the minimum propagation delay time. Consider the case that as shown in FIG. 11, a plurality of spread spectrum signals from a single spread spectrum signal transmitting station are passed along different propagation routes and received at terminal equipment as incoming waves 1 and 2 different in both propagation delay time and signal intensity. In this case, the delay profile received takes the shape of delay profile 12, a combination of delay profiles 10 and 11 corresponding to incoming waves 1 and 2, respectively. In this case, only receive timing 22 of incoming wave 2 can be detected with the prior art. In the example of FIG. 11, since incoming wave 1 has the minimum propagation delay time and is received in timing 21, receive timing for the incoming wave of the minimum propagation delay time cannot be measured using the prior art. As a result, receive timing measurement errors occur and this makes accurate distance or position measurement impossible.
For these reasons, the use of the present invention enables the distance between a signal transmitting station and a signal receiving station to be measured by creating a delay profile from the signal wave received from the signal transmitting station, then taking the startup timing of the delay profile as reference timing, and detecting the timing delayed by a predetermined value behind the reference timing.
To measure position, it is necessary to calculate the foregoing reference timing for at least three signal transmitting stations, then calculate the differences in send timing between the corresponding signal transmitting stations, and detect the position of the signal receiving station from the respective relative time differences.